The field of the invention is analog and/or digital display systems, and particularly, intelligent display systems for indicating successively occurring numerical values of a variable quantity.
There is a need to optically display the current or present value of a series of successively occurring numerical values of a variable quantity, such as a sequence of digitalized measured data values of a sensed or scanned variable quantity, for example, voltage, current, speed, temperature, and so on. The digitalization is performed, for example, by an analog-to-digital converter or by a counter converting measured input signals into digital output signals consisting of a sequence of numbers or numerical values having a more or less high degree of variations from one to the other value.
Generally, there are two basic types of display systems for optically indicating a series of successively occurring numerical values, namely analog or quasi-analog displays (hereinafter simply referred to as analog displays) and digital displays. While conventional analog display systems show the dynamics and trend of a sequence of measured values, the optical indication is of limited accuracy and/or optical resolution. While digital display systems provide a highly accurate optical indication with a high resolution, they present a rather irregular display upon the slightest variation of the digits so that it is neither possible to read the indicated values nor to identify the trend and dynamics of the variations.
There are in common use combined display systems having analog and digital displays. However, each one of the analog and digital displays is arranged so as to optically indicate the total measured value. Hence, the above mentioned drawbacks of each one of the two types of indicating and display systems are not overcome by combining them into a single module. Regarding prior art analog and digital display systems reference is made to a digital meter having an analog trend bar, for example, to a "HARMONY" meter manufactured by SIFAM LTD, Torquay, Devon, England.
Further, there are known digital display devices wherein the lowest digit position or two or more of the last digit positions are associated with an analog display or are substituted thereby in order to obtain a higher optical resolution by means of the additional analog display. Indicating systems of this type have the disadvantage that value variations which extend from the analog display into the digital display or vice versa are difficult to read and to interpret. Hence, the respective present instantaneous values are hardly readable.
In a display system as disclosed in laid-open German patent application No. 2 333 070, provisions are made to optically indicate the deviation of a measured value from a given desired value. The deviation is an error value which represents the difference value between the varying measured actual value and the given desired value. The error value is displayed in an analog manner by means of a transparent scale carrier, on the rear side of which several light-emitting zones are provided side by side. In response to the direction and magnitude of the error value a more or less large number of adjacent light-emitting zones are activated with reference to a mark provided on the scale carrier, which mark represents the given desired value. This known optical display system can indicate deviations or error values only which occur with reference to a fixed desired value. Besides, only more or less small error values or deviations from said fixed desired value can be displayed with sufficiently high accuracy and resolution since otherwise the range of the analog display is exceeded. On the other hand, when the indication of larger error values is allowed with respect to a scale carrier of given dimensions, the optical resolution of the analog display is reduced. Hence, the field of application of this known optical display system is rather limited.